Host immunocompetence and the influence of different treatment modalities on immunocompetence are very important issues in the treatment and prognosis of patients with prostatic cancer. Recently, we developed a unique assay for the measurement of cell mediated immunity (CMI) in both laboratory animals and human beings. Multiple lymphocyte reactivities can be measured in this assay such as: 1) level of natural killer cells, 2) mitogen stimulated cytotoxicity and 3) specific antigen stimulated cytotoxicity. It is our proposal to utilize this assay to measure CMI in untreated tumor patients and to determine, by longitudinal studies, the effect of various treatments on CMI. It is proposed that such studies may aid in the selection of optimal treatments and provide a basis for determining prognosis.